Microbial Induced Corrosion in Pipes
Microbial Induced Corrosion (MIC) in Pipes
All effective corrosion controls requires cleaning and passivation of the pipe reticulate then maintaining the appropriate alkalinity with maintenance dosage of chemical corrosion inhibitors and biocides. When the initial cleaning is not carried out appropriately, it will compromise the passivation that protects the base metal, the overall effectiveness of the initial high dosage of inhibitors at start up will be compromised. It is because the chemical corrosion inhibitors will not be able to forms a complete protective film on the metal surfaces. It will then be more likely to allow microorganism induced corrosion to develop in the years that follows; even with the recommended dosage of corrosion inhibitors, scale inhibitors and biocides during the monthly maintenance.
What does it likely to mean when you see black particulate that leaks from the Victaulic joints? It may be that the condenser pipe works and mechanical joints (Victaulic) were compromised by MIC. When MIC started below the gaskets in the joints it could not be stopped.
You will need to verify the following;
If the Victaulic seals is compatible for use with the chemical treatment regime undertaken, incompatibility may be evident by the black particles on the pipe external due to the breakdown of the seals by water treatment and pipes aggravated by MIC.
How to mitigate and reduce MIC in existing pipeworks;
Suitable chemical etch to clean the pipe internal surfaces, pressure clean to remove scale and biofilms, epoxy coated then passivise the pipes with high dosage of corrosion inhibitors and biocide. Record completed work with pipe camera visual inspections.
Before any works is carried out, care and due diligent will need to be taken into account for the following
1. Not to compromise and deteriorate the Victaulic seals.
2. Not to degrade any pipes and equipment
3. Not to compromise or clog coils by fugitive debris created during the cleaning
4. Comply with statutory requirements on all corrective works.
Note: It’s important to identify, assess, control and review risks associated with high pressure cleaning techniques.
Alternatively; replace the entire condenser water reticulate if it has a more favourable and sustained cost benefits outcome compared with proposals mentioned above. Ultimately it pays to do it right the first time to avoid costly premature failures.
What is MIC
MIC or microorganisms induced corrosion is due to heterotrophic microorganisms such as sulfide reducing bacteria (SRB), iron reducing bacteria (IRB) and acid producing bacteria (APB) in the water. MIC is metal deterioration as a result of the metabolic activity of various microorganisms. This type of corrosion applies to non-metallic objects as well as metals. Microbiologically influenced corrosion has previously been referred to as biological corrosion and microbial corrosion.
SRB are commonly considered the main culprits associated with anaerobic MIC due to the wide availability of sulfate (SO42−) in the aquatic environment. SRB’s are those bacteria that can live by oxidizing organic compounds or molecular hydrogen (H2) while reducing sulfate (SO42−) to hydrogen sulfide (H2S). In a sense, these bacteria breathe sulfate rather than oxygen in a form of anaerobic respiration. SRB’s, or their characteristic corrosion product FeS, are ubiquitously found on anaerobically corroded steel.
Biofilm and deposits also increase friction resistance against the water which leads to increase energy consumption to operate the circulating pumps. These biofilms also protect underlying bacteria from biocides and biocide treatment. It is important to remember, when the biocide is become depleted and biofilm is removed, the system will become re-contaminated from the bacteria in the system. So the next step should be the bacterial removal process. It is important to re-test after the corrective action is carried out and then every few years to ensure the effectiveness of the chemical treatment and presence of bacteria in the water.
It is also important to review the maintenance program with the water treatment specialists and schedule specially the actions required when there is no circulation of water. When there is no water circulation, there is more chance of MIC formation. SRB, IRB and APBs can be detected by water analysis.